Welcome to the Voice of America's News Words.
欢迎收看美国之音：新闻词汇。
This news word is from a story about flooding in the United States. Unprecedented.
今天的新闻词汇来自一个关于美国洪水的故事。前所未有的。
Rains from Hurricanes Harvey, Irma and Maria last summer caused unprecedented flooding in Puerto Rico and the states of Texas and Florida,
飓风哈维、伊尔玛和玛丽亚带来的降雨去年夏天在波多黎各、德克萨斯州和佛罗里达州造成了前所未有的洪水，
Experts say the storms have caused the most flooding since records on flooding began.
专家表示，暴雨已经导致自有记录以来最严重的洪灾。

Unprecedented is something that has not been done or experienced in the past.
史无前例是指在过去没有做过或经历过的事情。
It means having no precedent.
这意味着没有先例。
Precedent is something done or said that can served as a guide in the future.
先例是指将来可以作为指导的某件事或某句话。